Conventionally in order to enhance the sealing property of a mouthpiece of a container, prevent foreign objects from attaching to the mouthpiece of the container, ensure safety of the contents in the container in the case where the seal is broken by somebody, a wrapping member such as a cap seal or a shrink label is attached to a mouthpiece of a container having a cap.
In the case of attaching the wrapping member to the container, the mouthpiece of the container having the cap is surrounded by a cylindrical wrapping member, the size of which is slightly larger than that of the mouthpiece of the container. Then, the wrapping member is shrunk in the radial direction by heating so that the cylindrical wrapping member can be tightly contacted with an outer circumferential face of the mouthpiece of the container.
At the time of heating the wrapping member, a hot air type heating device for blowing hot air onto the wrapping member is widely used. For example, according to the hot air type heating device disclosed in Japanese Unexamined Patent Publication No. 2003-291926, a container surrounded by a wrapping member is made to pass through a tunnel-shaped heating chamber so as to preheat the wrapping member in the heating chamber. After that, a hot air of a predetermined temperature is blown to the wrapping member, so that the wrapping member can be shrunk by heat shrinkage. For details, refer to Japanese Unexamined Patent Publication No. 2003-291926.
However, the hot air type heating device of the related art, which is disclosed in Japanese Unexamined Patent Publication No. 2003-291926, is disadvantageous in that it is difficult to uniformly shrink the wrapping member in the circumferential direction. As a result, the wrapping member is attached to a mouthpiece of a container while being inclined in some cases. Alternatively, wrinkles or color unevenness is caused in the wrapping member after it has been attached to the mouthpiece of the container.
Recently, it is common to use a wrapping member, the length in the longitudinal direction of the container of which is relatively long. Further, it is common to use a wrapping member such as a cap seal or a shrink label on which letters or pictures are printed. Accordingly, the wrapping member is attached to the mouthpiece while being inclined or it wrinkles and/or color unevenness is caused in the wrapping member, information included in the design of the wrapping member cannot be accurately notified to a consumer, which affects sales of the containers to which the above wrapping member is attached.
In the case where the container and the wrapping member are gradually heated while suppressing a rise in the temperature per unit time, it is possible to prevent a wrapping member from being tilted when it is attached to the container. Further, it is possible to prevent the generation of wrinkles and/or color unevenness. However, in this case, it is necessary to extend the length of a conveyor for conveying the containers at the time of heating. Alternatively, it is necessary to reduce a conveyance speed of conveying the containers by the conveyor. Therefore, additional expenses are required or throughput will be lowered, which are not preferable.
The present inventors made investigations into the cause of the generation of wrinkles and color unevenness on the wrapping member after the wrapping member has been attached to the mouthpiece of the container. As a result of their investigations, the present inventors obtained the following knowledge. In the related art, the container and the wrapping member are simultaneously heated by the hot air type heating device. Therefore, at the time of heating, heat is mainly absorbed by the container and a hot air is blown to the wrapping member only in one direction or only in a plurality of directions. Thus, it is difficult to uniformly heat the wrapping member in the circumferential direction. Due to this, wrinkles and color unevenness are caused. According to the above knowledge, the present inventors investigated and obtained knowledge in which the above problems can be solved by preheating the container and then attaching the wrapping member to the preheated container, and accordingly, the present invention has been accomplished. In other words, the present invention has been accomplished in view of the above circumstances. An object of the present invention is to provide a wrapping member attaching method capable of attaching a wrapping member to a container without causing an inclination attaching of the wrapping member and without generating wrinkles and/or color unevenness on the wrapping member. Another object of the present invention is to provide a wrapping member attaching device for executing the wrapping member attaching method.